Abstract
By the end of the nineteenth century, biostratigraphy had come to be thought of as a matter of induced extinctions, of varying severity, subsequent to which some surviving species would go on to generate forms adapted to the changed Earth environment. John Phillips', proposal from 1841, that the systems comprising the biostratigraphical record could be packaged into three eras—Palaeozoic, Mesozoic and Cenozoic—recognized that the end Permian and end Cretaceous were defined by extinctions that globally eliminated a large proportion of the previously abundant and long‐lived terrestrial and marine taxa. These two key horizons are now seen as defining two of a series of at least five Phanerozoic global mass extinctions, each of which suggested a short‐lived major disruption of the entire biosphere.